5.2. Accessibility

Some users may need specific support because of e.g. some visual
impairment.
USB braille displays are detected
automatically (not serial displays connected via a serial-to-USB converter),
but most other
accessibility features have to be enabled manually.
On machines that support it, the boot menu emits beeps
when it is ready to receive keystrokes. It beeps once on BIOS systems,
and beeps twice on UEFI systems.
Some boot parameters can then be appended to
enable accessibility features (see also
Section 5.1.7, “The Boot Screen”).
Note that on most architectures the boot loader interprets your keyboard as
a QWERTY keyboard.

5.2.1. Installer front-end

The Debian installer supports several front-ends for asking questions, with
varying convenience for accessibility: notably, text
uses plain text while newt uses text-based dialog
boxes. The choice can be made at the boot prompt, see the documentation for
DEBIAN_FRONTEND in Section 5.3.2, “Debian Installer Parameters”.

5.2.2. USB Braille Displays

USB braille displays should be automatically detected. A textual version
of the installer will then be automatically selected, and support for the
braille display will be automatically installed on the target system.
You can thus just press Enter at the boot menu.
Once brltty is started, you can choose a braille
table by entering the preference menu. Documentation on key
bindings for braille devices is available on the brltty website.

5.2.3. Serial Braille Displays

Serial braille displays cannot safely be automatically detected
(since that may damage some of them). You thus need to append the
brltty=driver,port
boot parameter to tell brltty which driver and port it
should use. driver should be replaced by the
two-letter driver code for your terminal (see the
BRLTTY manual).
port should be replaced by the name of the
serial port the display is connected to, ttyS0 is
the default, ttyUSB0 can be typically used when using a serial-to-USB converter.
A third parameter can be provided, to choose the name of the
braille table to be used (see the BRLTTY
manual); the English table is the default. Note that the table can
be changed later by entering the preference menu. A fourth parameter
can be provided to pass parameters to the braille driver, such as
protocol=foo which is needed for some rare models.
Documentation on key
bindings for braille devices is available on the brltty website.

5.2.4. Software Speech Synthesis

Support for software speech synthesis is available on all installer images which
have the graphical installer, i.e. all netinst, CD and DVD images, and the
netboot gtk variant. It can be activated by selecting it in the
boot menu by typing sEnter. The textual version
of the installer will then be automatically selected, and support for software
speech synthesis will be automatically installed on the target system.

The first question (language) is spoken in english, and the remainder
of installation is spoken in the selected language (if available in
espeak).

The default speech rate is quite slow. To make it faster, press
CapsLock+6.
To make it slower, press
CapsLock+5.
The default volume should be medium. To make it louder, press
CapsLock+2.
To make it quieter, press
CapsLock+1.
To get more details on the browsing shortcuts, see the
Speakup guide.
To just accept the default answer for a question, simply press
Enter at the prompt.
To provide an empty answer for a question, type ! at the
prompt.
To get back to the previous question, type < at the
prompt.

5.2.5. Hardware Speech Synthesis

Support for hardware speech synthesis devices is available on all installer
images which have the graphical installer, i.e. all netinst, CD and DVD images,
and the netboot gtk variant. You thus need to select a “Graphical
install” entry in the boot menu.

Hardware speech synthesis devices cannot be automatically detected. You
thus need to append the
speakup.synth=driver
boot parameter to tell speakup which driver it should
use. driver should be replaced by the driver code
for your device (see driver code
list). The textual version of the installer will then be
automatically selected, and support for the speech synthesis device will be
automatically installed on the target system.

5.2.6. Board Devices

Some accessibility devices are actual boards that are plugged inside the
machine and that read text directly from the video memory. To get them
to work framebuffer support must be disabled by using the
vga=normalfb=false
boot parameter. This will however reduce the number of available languages.

If desired a textual version of the bootloader can be activated before adding
the boot parameter by typing hEnter.

5.2.7. High-Contrast Theme

For users with low vision, the installer can use a high-contrast
color theme that makes it more readable. To enable it, append the
theme=dark boot parameter.

5.2.8. Zoom

For users with low vision, the graphical installer has a very basic zoom support: the
Control++ and
Control+- shortcuts
increase and decrease the font size.

5.2.9. Expert install, rescue mode, automated install

Expert, Rescue, and Automated installation choices are also available
with accessibility support. To access them, one has to first enter the
“Advanced options” submenu from the boot menu by typing
a. When using a BIOS system (the boot menu will
have beeped only once), this has to be followed by Enter. Then, to
enable speech synthesis, s can optionally be pressed
(followed again by Enter when using a BIOS system). From there, various
shortcuts can be used: x for expert installation,
r for rescue mode, or a for
automated installation. When using a BIOS system, they must be followed by
Enter.